This invention relates to a process for making a granular detergent product and the product of the process. More particularly, the invention relates to a process for preparing detergent compositions which are useful in automatic dishwashing machines.
Detergent compositions comprising, in combination, alkaline salts such as sodium silicate and sodium carbonate, an alkaline polyphosphate such as sodium tripolyphosphate, a surfactant and a chlorine containing compound that provides hydrochlorite ion in solution have particular utility for machine dishwashing. The formulation of such compositions made of agglomerates of the ingredients has been generally accomplished by the addition of an aqueous sodium silicate solution and liquid surfactants to a mixture of dry ingredients. Compositions prepared in such manner, however, are characterized by a tendency to cake in their cartons during storage and can also have a tendency to cake in the dispenser cups of dishwashing machines. A number of process modifications have been suggested to control the agglomeration process and reduce the caking tendency of detergent compositions prepared using silicate solutions and liquid surfactants as agglomerating agents. U.S. Pat. No. 2,895,916 discloses an order of addition in which the chlorine containing compound, chlorinated trisodium phosphate, is added to the composition only after the aqueous silicate has been added to the polyphosphate. The benefit is said to result from a more rapid hydration of the sodium tripolyphosphate in the absence of chlorinated trisodium phosphate. U.S. Pat. No. 3,741,904 discloses the preparation of a protected granule by addition of an aqueous solution of a nonionic surfactant of dry components including polyphosphates before addition of a silicate solution.
U.S. Pat. Nos. 3,247,118; 3,520,815; 3,600,317; and 3,888,781 also disclose the effect of process variations such as order of ingredient addition on the physical characteristics of a granular detergent product.
Typical automatic dishwashing product compositions contain from about 1/2% to about 3% of nonionic surfactants, generally in combination with a suds control agent. As disclosed in copending commonly assigned U.S. patent applications Ser. Nos. 849,132 and 902,577, incorporated herein by reference, the use of relatively higher surfactant levels is particularly beneficial in compositions containing less than about 35% sodium tripolyphosphate. In the conventional process of agglomerating sodium tripolyphosphate with aqueous sodium silicate solutions, it is convenient and satisfactory to spray on or otherwise add a liquid nonionic surfactant at any time during the agglomeration process. It has been found, however, that addition of levels of a liquid alkoxylated nonionic surfactant above about 4% in the conventional manner results in either a complete inability to produce the product or in unacceptable product physical properties, particularly with respect to carton caking after exposure to elevated temperatures or caking in dishwashing machine dispenser cups. The physical properties of an agglomerated granular detergent composition containing sodium tripolyphosphate is closely related to the complex hydration characteristics of sodium tripolyphosphate which is in turn dependent on particle size, water content and temperature conditions during manufacture.
A so-called Form I is produced if the process of manufacture includes a relatively high temperature calcination step. A Form II results when lower temperatures are employed. Form I is characterized by relatively rapid hydration characteristics. Form II, particularly in the absence of any substantial level of Form I material is slow to hydrate, but has a greater immediate solubility. Commercially available sodium tripolyphosphate is generally a mixture of Form I and Form II. U.S. Pat. Nos. 2,622,068; 2,961,409 and 2,961,410, incorporated herein by reference disclose the characteristics of Form I and Form II sodium tripolyphosphate in the manufacture of spray-dried detergents.
The processes known in the prior art have not proven to be entirely satisfactory for the production of agglomerated granular detergents containing relatively high levels (i.e., from about 4% to about 20%) of alkoxylated nonionic surfactants, particularly when the surfactant is liquid at ambient temperatures and more particularly for compositions containing less than about 35% sodium tripolyphosphate on an anhydrous basis.
It has now been found that an agglomeration process for producing detergent compositions containing at least about 10% sodium tripolyphosphate, from about 4% to about 20% of an alkoxylated nonionic surfactant, an alkali metal silicate and optionally a compound providing hypochlorite ions in aqueous solution can be optimized if part of the nonionic surfactant is added to the tripolyphosphate and part is added to dry ingredients other than polyphosphate.
Accordingly, it is an object of this invention to produce agglomerated granular detergent compositions containing from about 4% to about 20% of an alkoxylated nonionic surfactant with improved physical properties.
Other objects and advantages will be apparent from the following description and examples.